This kind of slat conveyor is one in which left and right both side faces of each slat body are pivotally supported, by horizontal support shafts, to a pair of left and right driving endless turning bodies turning along a circulation path composed of an upper horizontal outward path section, a lower horizontal inward path section, and U-turn path sections at both ends. In general, two forms of slat conveyor are known. The first form is one that positions of the pair of left and right driving endless turning bodies are shifted in the front-rear direction and pivotal support positions of the slat body with respect to the pair of left and right driving endless turning bodies are also shifted in the front-rear direction in conformity with the pair of left and right driving endless turning bodies. The second form is one that the pair of left and right driving endless turning bodies are disposed bilaterally symmetrically and each slat body is pivotally supported between the pair of left and right driving endless turning bodies by mutually concentric horizontal support shafts. The present invention relates to improvements of the latter second form of slat conveyor. As described in Patent Literature 1 (Japanese Unexamined Utility Model Application Publication No. S53-2350), a conventional slat conveyor of this kind has a configuration that the left and right both side faces of each slat body are provided with a third roller positioned outside the pair of left and right driving endless turning bodies in addition to a pair of front and rear guide rollers rolling along a guide rail disposed along each of the upper and lower horizontal path sections, and a slat body posture controlling rotating body interlockingly rotating with the driving endless turning bodies is pivotally supported outside the driving endless turning bodies on the U-turn path sections at both ends, and the third roller is engaged with the slat body posture controlling rotating body to make each slat body U-turn parallelly while being maintained in the horizontal posture on the U-turn path sections at both ends.